Coherence Phenomena In Atoms And Molecules In Laser Fields

This volume presents the latest advancements and future perspectives of atomic, molecular and optical (AMO) physics and its vital role in modern sciences and technologies. The chapters are devoted to a wide range of quantum systems, with an emphasis on the understanding of ionization, high-harmonic generation, molecular orbital imaging and coherent control phenomena originating from light-matter interactions. The book overviews current research landscape and highlight major scientific trends in AMO physics interfacing with interdisciplinary sciences. It may be particularly interesting for young researchers working on establishing their scientific interests and goals.

This volume contains the lectures and communications presented at the NATO Advanced Research Workshop (NATO ARW 900857) which was held May 5-10, 1991 at McMaster University, Hamilton, Ontario, Canada. A scientific commitee made up of P.P. Lambropoulos (USC & Crete), P.8. Corkum (NRC, Ottawa), and H. B. vL. van den Heuvell (FOM, Amsterdam) guided the organizers, A.D. Bandrauk (Sherbrooke) and S.C. Wallace (Toronto) in preparing a programme which would cover the latest advances in the field of atom and molecule laser interactions. Since the last meeting held in July 1987 on "Atomic and Molecular Processes with Short Intense Laser Pulses", NATO ASI vol 1718 (Plenum Press 1988), considerable progress has been made in understanding high intensity effects on atoms and the concomitant coherence effects. After four years, the emphasis is now shifting more to molecules. The present volume represents therefore this trend with four sections covering the main interests of research endeavours in this area: i) Atoms in Intense Laser-Fields ii) Molecules in Intense Laser Fields iii) Atomic Coherences iv) Molecular Coherences The experience developed over the years in multiphoton atomic processes has been very useful and is the main source of our understanding of similar processes in molecules. Thus ATI (above threshold ionization) has been found to occur in molecules as well as a new phenomenon, ATD (above-threshold dissociation). Laser-induced avoided crossings of molecular electronic surfaces is also now entering the current language of high intensity molecular processes.

This text presents the major advances in both intense laser fields phenomena and laser control of photochemical reactions - highlighting experimental and theoretical research on the interaction of simple molecules with intense laser fields. The book introduces new concepts such as above-threshold ionization (ATI), above-threshold dissociation (ATD), laser-induced avoided crossings, and coherent control.

The rapid development of powerful pulsed lasers is at the origin of a conside rable interest in studying the response of an atom, a molecule (or a solid) to a strong electromagnetic field. It is now possible to produce at the laboratory scale, ultra-short 13 pulses with a duration of 100 femtoseconds (10- second) and a power of the order 12 of 1 terawatt (10 Watt). Under these conditions, very high peak intensities may be obtained and electric fields exceeding typical electron binding fields in atoms are generated. The interaction of an atom or a molecule with such electromagnetic fields has a highly non-linear character which leads to unexpected phenomena. Amongst them, - above-threshold ionization (ATI) i.e. the absorption of additional photons in excess of the minimal number necessary to overcome the ionization potential and its molecular counterpart, above-threshold dissociation (ATD); - generation of very high harmonics of the driving field; - stabilization of one-electron systems in strong fields. These processes were the main topics of two international meetings which were held in 1989 and 1991 in the United States under the common name SILAP (Super-Intense Laser-Atom Physics).

Lectures presented in this book reflect well the new results and new problems which attract the attention of both experimentalists and theorists working in the field of physics of multiphoton processes in atoms and molecules.

The aim of this NATO Advanced Study Institute was to bring together scientists and students working in the field of laser matter interactions in order to review and stimulate developmentoffundamental science with ultra-short pulse lasers. New techniques of pulse compression and colliding-pulse mode-locking have made possible the construction of lasers with pulse lengths in the femtosecond range. Such lasers are now in operation at several research laboratories in Europe and the United States. These laser facilities present a new and exciting research direction with both pure and applied science components. In this ASI the emphasis is on fundamental processes occurring in the interaction of short laser pulses with atoms, molecules, solids, and plasmas. In the case of laser-atom (molecule) interactions, high power lasers provide the first access to extreme high-intensity conditions above 10'8 Watts/em', a new frontier for nonlinear interaction of photons with atoms and molecules. New phenomena observed include multiphoton ionization processes, atomic collisions in the presence of a strong laser field, Coulomb explosion following rapid ionization of a molecule and the production of high harmonics of the laser source. Another important topic reviewed in this ASI is the lasercooling ofatoms.